This project investigates endogenous and exogenous factors that contribute to the development of cognitive and social competencies in children during the first four years of life. Before children are old enough to enter formal social learning situations, nearly all of their experiences stem directly from interactions they have with their primary caregivers. The present study focuses on the extent to which several maternal characteristics (age, parenthood status, SES, parity, employment status, as well as type of substitute care experienced during mother~s employment) influence observed relations between caregiving on the one hand and child developing cognitive and social competencies on the other. In this longitudinal study, subjects are visited when they are 5, 20, and 48 months of age. At 5 months, mother-infant interaction is observed. At 20 months, measures of toddler functioning (play competence, language development, and social adaptation) and maternal behavior (play and intelligence) are obtained. At 48 months, the follow-up examines diverse children's abilities (representational competence, problem solving, reasoning skills, mathematical ability, language use and discourse, and selected aspects of generally adaptive behavior).